Not applicable.
Not applicable.
The present invention relates to the field of object stacking and more particularly to a system and method for stacking substantially flexible objects. The objects may also be substantially flat and further comprise mail pieces, although application of the present invention is not related to just mail handling. For purposes of illustration only, the present invention will be described with respect to a first non-limiting application to mail pieces. The mail pieces are stacked standing in a stacker with their narrow side facing forward. The successively and individually supplied mail pieces are routed to a movable installation wall against which they lean with their side wall facing the installation wall. In this position, the mail pieces are further stacked in a stack with their front edge facing forward against an impact wall. The stacking process is aided by a stacking roller.
Mail pieces come in a wide variety of formats (lengths, heights, widths, flexibilities, etc.). Normal mail handling entails successive mail piece transport in relatively close succession. Such transport general occurs with the mail pieces sandwiched between elastic straps. It is necessary to get the back edge of a forward mail piece out of the way of the front edge of a trailing mail piece. This is effected by a so-called xe2x80x9cclearing of the insertion trianglexe2x80x9d during stacking.
To facilitate stacking, a powered stack spindle is set out in DE 3 317 865 A1. The spindle is located closely in front of each stacker and deflects the objects in the direction of movement to the stack. Accordingly, successive objects do not meet with the rear edges but sideways with the already stacked objects. The power introduction occurs at the lower edge of the objects. This results in twistings of particularly high objects because of mass reactance, i.e. the upper rear edge doesn""t clear the xe2x80x9cinsertion trianglexe2x80x9d on time or at all.
Additional deflection elements, for example pivoting levers which are similar to diverter vanes, are known from U.S. Re. 34,330. The deflection element is hereby designed as a counter current diverter element, i.e. the tip directs opposite the direction of transport of the objects in motion. If the deflecting element is not engaged before it is reached by the front edge of an object, it collides frontally with the object which can lead to its destruction.
With these known solutions, the power introduction point lies at a respectively determined location. The functionality of certain lengths of objects is thereby limited. With mail pieces which are too long, the distance between the rear edge of the object and the power introduction point is often too large. The objects deform, conditioned on their mass reactance, their rear edge is not brought out from the insertion triangle, and there is the risk of a collision with a successive object. With objects which are too short, the rear edge is met partially or not at all by the function element which introduces power. Accordingly a need exists in the art to facilitate better operation of the insertion triangle while accommodating a widest possible variety of object format.
The present invention is directed to addressing the above needs. An advantage of the present direction is its use of relatively generic devices thereby enjoying a wide applicability. The present invention concerns a generic device for the stacking of flat, flexible, on a narrow side standing objects, into a stacker which guarantees a mostly trouble free stacking without collision of rear and front edges of successive objects. Application of the present invention is also found with objects of a wide length and format spectrum.
These and other advantages are solved by a system CLAIM 1.
The present system makes use of deflecting elements strategically placed in succession along the conveyance path of the objects. The deflecting elements generally engage the rearward parts of the objects (with respect to conveyance direction). A determination is made of the space or distance between successive objects. The selection and prior known speed of conveyance allows for the determination of location and time of arrival. Accordingly, the deflection elements can be selectively triggered to engage the objects at specific locations. This accommodates objects of different format. In operation, a rearward part of the object is deflected by the deflecting element as a front part enters a stacking roller area. Accordingly, collision between successive objects is avoided.
It is further advantageous, to determine the starting time of the deflection movement of the determined respective deflecting element in such a way that a contact point between the deflecting element and the object doesn""t exceed a maximal distance of the rear edge. It is thereby avoided that very flexible, thin objects, don""t bend around the contact point and that the rear edge remains approximately in the non-deflecting position.
It is also advantageous, to realize the deflecting elements as diverter vanes, whose tip points in a conveyance direction in a non-deflecting condition or position (co-current diverter). A frontal collision of the objects with the diverter vane is thereby avoided as it would be possible at a diverter of a counter current diverter.
If the diverter vane is applied in such a way that the sides diverge and the tip forms an arc of a circle, so that there is no free space between the diverter vane and guide during deflection, an object rebound from an impact wall can not get into a spacing and get jammed.
In a further advantageous design, elastic and/or an elastically fixated conveyor roller is placed in the conveying path associated with a stacker. The roller presses the objects against the guide and rotates in a conveying direction at a relative transport speed. The distance of the conveyor roller from the impact wall is shorter than the longest objects. In operation, the long objects, if they are braked but are further transported by the conveyor roller, are bent in the middle in an installation wall/stack direction. If the rear edge then leaves the conveyor roller, the rear part of the long object is then thrown in a stack direction by the conveyor roller and due to internal stress from deflection.
In order to avoid unwanted contact of the deflecting elements with the successive objects, time and duration of the deflections of the deflecting elements are determined in such a way that the deflecting elements will have reached a resting position before the next object comes along.
If no object is stacked for a longer period of time, i.e. no objects come into the area of the deflecting elements, it is advantageous, to leave the deflecting elements in the non-deflecting position during this time, to avoid that the rear part of the stacked objects move backwards into the xe2x80x9cinsertion trianglexe2x80x9d because of weights or internal stresses.